Giles Barr

Abstract:

The "neutral" trigger system for the selection of K-o --> 2 pi(o) --> 4 gamma decays of the NA48 CP-violation experiment is described. The trigger system has been implemented in a 40 MHz "dead-time free" pipeline to allow large rate reduction and high-trigger efficiency. The trigger decision is based on the information from 13340 cells of the electro-magnetic calorimeter. Every 25 ns the energy, the centre of gravity, the kaon lifetime and the number of peaks in calorimeter projections are calculated in the trigger. The pipeline system is described and the performance of the trigger during the 1997 data-taking period is discussed. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

The 13500 channels of the NA48 liquid-krypton electromagnetic calorimeter readout electronics were put into operation in 1997. The digitizer electronics employs a new gain switching technique that expands the dynamic range of a standard 10-bit ADC to 14 bits at 40 MHz sampling rate employing a custom-developed integrated circuit (KRYPTON). The KRYPTON has been fabricated in 1.2 mu m BiCMOS technology and was successfully developed together with industry on a short timescale. The performance and the experience from the first year of the operation of the liquid-krypton calorimeter electronics will also be briefly discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

A first level trigger system based on a 40 MHz digital pipeline has been developed for the CERN NA48 [1] experiment, aiming at measuring CP violation in K-0 --> 2 pi decays.The outputs of the 13340 cells of the 10 m(3) liquid krypton calorimeter are summed into 64 X and 64 Y projection strips and continuously digitised with 40 MHz FADCs.This information is used to reconstruct at each clock cycle and for the two calorimeter projections, the number of clusters, the impact time of each of them (with a precision of about 3 ns), their total energy and the first and second moments of the energy distribution.Based on the quantities listed above, a programmable look-up table system subsequently computes online the longitudinal position of the kaon decay vertex and performs an event selection.The system is described.